The Pima Indians are a group of people with a very high incidence of obesity, which is already developing in the children and adolescents of this population. Adipose cell metabolism has been studied extensively in rodents. The current obesity studies are an extension of the rodent work with a population of people that can be studied longitudinally as well as cross-sectionally. Initially we have focused on the adult population characterizing the adipose cell size and number of this population, and have shown that after cell size increased beyond a certain point, any further increase in adiposity is accounted for by an increase in adipose cell number. In addition, comparisons between Pimas and Caucasians regarding the generating of obesity are being made to establish whether any differences in adipose cell metabolism between and two populations can be elucidated. We have also studied the effect of fasting as a function of obesity to determine whether the ability to mobilize fat can be correlated with obesity and adipose cell size and number correlate with the appearance of insulin resistance in this population. A better understanding of this relationship if important for both the study of obesity and diabetes.